Rational, Fixnum#power! and negative values

ruby-talk
1

Hi all,

Another question about Rational#power!. I tried this

irb(main):001:0> 2.power!(-2)
NoMethodError: undefined method `power!' for 2:Fixnum
         from (irb):1
irb(main):002:0> require 'rational'
=> true
irb(main):003:0> 2.power!(-2)
=> 0.25 # huh?

That returns 0.25. However, I would have expected Rational(1, 4). Based on the code in rational, it looks like power! is an alias for **, and ** is an alias for rpower. So, based on the rpower method, I would think that a negative value for +other+ would call Rational.new! and return a Rational.

Or do I have it wrong?

from rational.rb:

class Fixnum
   undef quo
   # If Rational is defined, returns a Rational number instead of a Fixnum.
   def quo(other)
     Rational.new!(self,1) / other
   end
   alias rdiv quo

   # Returns a Rational number if the result is in fact rational (i.e. +other+ < 0).
   def rpower (other)
     if other >= 0
       self.power!(other)
     else
       Rational.new!(self,1)**other
     end
   end

   unless defined? 1.power!
     alias power! **
     alias ** rpower
   end
end

Ideas? Thanks.

Dan

2

Daniel Berger wrote:

Hi all,

Another question about Rational#power!. I tried this

irb(main):001:0> 2.power!(-2)
NoMethodError: undefined method `power!' for 2:Fixnum
         from (irb):1
irb(main):002:0> require 'rational'
=> true
irb(main):003:0> 2.power!(-2)
=> 0.25 # huh?

That returns 0.25. However, I would have expected Rational(1, 4). Based on
the code in rational, it looks like power! is an alias for **, and ** is an
alias for rpower. So, based on the rpower method, I would think that a
negative value for +other+ would call Rational.new! and return a Rational.

Or do I have it wrong?

from rational.rb:

class Fixnum
   undef quo
   # If Rational is defined, returns a Rational number instead of a Fixnum.
   def quo(other)
     Rational.new!(self,1) / other
   end
   alias rdiv quo

   # Returns a Rational number if the result is in fact rational (i.e. +other+
< 0).
   def rpower (other)
     if other >= 0
       self.power!(other)
     else
       Rational.new!(self,1)**other
     end
   end

   unless defined? 1.power!
     alias power! **
     alias ** rpower
   end
end

Ideas? Thanks.

Dan

power! is an alias of Fixnum::**, then ** is reused as an alias of
rpower
So calling power! is not invoking rpower, it is invoking the original
Fixnum:**

Took me a while to figure that out, the alias'ing does at first glance
look like it would chain the methods as you expected

Cheers